The complex conjugate of $\displaystyle{a}+{b}{i}\usepackage{cmbright}\Huge\$ is $\displaystyle{a}-{b}{i}\usepackage{cmbright}\Huge\$ . Therfore the complex conjugate of $\displaystyle{7}-{3}{i}\usepackage{cmbright}\Huge\$ is $\displaystyle{7}+{3}{i}\usepackage{cmbright}\Huge\$ .